Among α,β-unsaturated carboxylic acid or α,β-unsaturated carboxylic ester, particularly important methacrylic acid and methyl methacrylic ester have conventionally been produced widely through a route via acetone cyanohydrin obtained by reacting acetone with hydrocyanic acid.
There was also disclosed a method of producing α,β-unsaturated carboxylic acid or ester by contacting a carboxylic acid, carboxylic ester or carboxylic anhydride with formaldehyde or formaldehyde source by using a catalyst containing niobium oxide (JP2001-507697W, which is an equivalent of WO98/29379). In this method, however, moisture sensitive and expensive niobium fluoride was required. A method of producing acrylic acid or methacrylic acid using a solid catalyst having an acid site having acid strength of pKa≦−3.0 has been proposed (see JP-A-60-246342, which is equivalent of U.S. Pat. No. 4,677,225) and particularly disclosed therein is a method of using silica alumina containing Al2O3 in the amount of 13 to 28%, which showed insufficient selectivity.